I think people's motivations for writing fiction - novels - could be reduced to six.
Some of these motivations are simple to understand - 'get rich', 'get recognised', 'sheer pleasure', 'because your failed author parents want you to repeat their folly' and so on. I have seen 'there are only n types of plot' stories before, I would much rather have motivations for writing novels being the categorisation as then I would be able to better identify what I did want to read, i.e. the 'banned books'.
There is a big difference between what some Eton educated aristocrat dictates to their secretary so they can be lauded in society as an 'author' to what someone in jail with no education writes to get themselves their freedom. This applies to words beyond novels too. For example the 'left wing' writings of Tony Benn (UK anti-war movement, aristocrat, dictated to secretaries) matter very little to me compared to what Malcolm X had to say.
New stories that don't necessarily fit into pigeonholes can come from real life where that period of history is a bit of a lie and the truth can't be told under any circumstances. During these times the only truth can be found in novels that transpose the names, times and places for something that the audience won't self-censor. So we end up with 'Oceania' or 'Animal Farm' with it not being clear what regime is being critiqued exactly.
Such works of fiction are written because something needs to be said, or at least the author thinks so. It is not like the author has decided 'I want to become a writer' and googled a plot from the internet to rip off. In this way literature is written, not just novels to make money with.